Hi, you could combine a function and a sed statement to create a way of changing a field value based on a field name. E.g.

Code:

replace_field() 
{
  sed "/^$1/s/\(${2%=*}=\)[^|]*/\1${2#*=}/" infile;
}
replace_field "title=Boston" "desc=bla bla"

Code:

output:
title=Boston|tcolor=green|desc=bla bla|url=http://www.boston.com
title=New York|tcolor=gold|desc=The largest city on the East Coast|url=http://www.newyork.com
title=Dallas|tcolor=silver|desc=A sprawling, cheery Texas city|url=http://www.dallas.com

This probably looks quite cryptic but it is based on the previous examples with the values replaced by $2 (and parameter expansions). The function takes the first key to locate the line on which certain fields need to be replaced.

We can expand this to take more fields and replace the $2 expansions with field names so it becomes a bit more readable..

Code:

replace_fields() 
{
  key="$1"; shift
  sedstr="/^$key/{"
  while [ $# -gt 0 ]; do
       field="${1%=*}"
       val="${1#*=}"
       sedstr="${sedstr}s/\b\($field=\)[^|]*/\1$val/;"
       shift
  done
  sedstr="$sedstr}"
  sed "$sedstr" infile
}

replace_fields "title=New York" "tcolor=green" "desc=blabla"

Output:

Code:

title=Boston|tcolor=green|desc=Large city in New England|url=http://www.boston.com
title=New York|tcolor=green|desc=blabla|url=http://www.newyork.com
title=Dallas|tcolor=silver|desc=A sprawling, cheery Texas city|url=http://www.dallas.com

If you want to edit the file directly
you could use:

Code:

sed -i "$sedstr" infile

if your sed supports it or

Code:

sed "$sedstr" infile > /var/tmp/infile.tmp.$$ && mv /var/tmp/infile.tmp.$$ infile

It builds a sed statement based on the inout fields that are being provided. Unfortunately I haven't been able to make it simpler than this.

Also, it has to be said that this will probably only work in very low intensity situations. If more users will be creating updates simultaneously then problems may occur and you will have to create some sort of locking-and-wait mechanism. If it is getting more serious you will probably be better off using a simple database.